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Genetics
- Question
- How can you explain that only one in four children has CF and not all children?
- Answer
- CF or cystic fibrosis is an inheritable recessive disease.
First some general information: the genetic code for all proteins in our body are present in the genetic material of every cell in the body and these codes are called genes, present in our chromosomes. When a protein is synthesized, this code is translated to a protein by special “machines” in the cell. The protein affected in cystic fibrosis has a special function, namely transport of salt. A wrong code of the gene on the chromosome can result in decreased function or complete absence of function. This is what we call a genetic disease: the diseased person can also transmit the wrong code to his kindred.
The abnormal code of the CF gene in cystic fibrosis results in disturbed transport of salts on the mucosal level and this leads to dehydrated mucus. Cystic fibrosis is an ‘autosomal recessive’ disease. ‘Autosomal’ means that the genetics are independent of the sex (it’s as frequent in boys as in girls). ‘Recessive’ means that a patient with CF inherited the abnormal gene from both parents and has no normal copy of the CF gene. It means that in a recessive disease two abnormal genes are needed for the disease to occur. Parents of the child with CF are always carrier of a normal gene and a CF gene. In the sperm or the ovule, only half of the genetic material is present: it’s or the normal gene, or the CF gene. At conception the sperm and the ovule are fused. The following four combinations of gene can thus occur once the sperm and the ovule fuse: twice normal (1 chance out of 4), normal and diseased (1 chance out of 4), diseased and normal (1 chance out of 4, together with the previous option this is 1 out of 2 and this is called carrier ship), twice diseased (1 chance out of 4). All together there is thus one chance out of 4 that a combination is formed whereby the 2 genes are diseased and only the latter combination results in a child with cystic fibrosis. Of course, for every conception, the child of 1 out of 4 holds through.
Dr. P. Van De Wijdeven
- 23.03.2010
